[The immune state against yellow fever vaccinal virus (17D) in 2 populations of Bahia State, Brazil].

The occurrence of cases of yellow fever (YF) and also the extensive distribution of A. aegypti in Brazil, inspired a study about the estimate of immunity against vaccinal virus (17D) among the residents at two cities of the Bahia State, Ipupiara (n = 461) and Prado (n = 228). At this non-endemic area of YF, the search for serology antibody against 17D (Ab17D) and 18 another arbovirus was made thereby hemagglutination inhibition (HI). Only 1.2% (8/689) showed Ab17D, six of those with monotypic sort. The heterotypic sort for flavivirus (FLV) was interpreted as associated to immunity against 17D too, being much frequent in Prado (30.3%) than in Ipupiara (23.2%). The age > or = 50 years and residence in another states were related to seropositive for FLV, the same way that vaccination's history (17D). However, the history of vaccination presented low percentages of sensibility (< or = 45.4%) and predictive-positive value (< or = 38.4%), but high specificity (> or = 70.8%) and predictive-negative value (> or = 78.8%). Therefore, the frequency of residents with Ab17D was low (1.2%), although the higher frequency (25.5%) of antibody FLV carrier's, what signifies that 26.7% of the studied population should present protection against the YF virus.